/*-------------------------------------------------------------------------
 *
 * joinutils.c--
 *    Utilities for matching and building join and path keys
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /usr/local/cvsroot/postgres95/src/backend/optimizer/path/joinutils.c,v 1.1.1.1 1996/07/09 06:21:36 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "nodes/pg_list.h"
#include "nodes/relation.h"
#include "nodes/plannodes.h"

#include "optimizer/internal.h"
#include "optimizer/paths.h"
#include "optimizer/var.h"
#include "optimizer/keys.h"
#include "optimizer/tlist.h"
#include "optimizer/joininfo.h"
#include "optimizer/ordering.h"


static int match_pathkey_joinkeys(List *pathkey, List *joinkeys,
		 int which_subkey);
static bool every_func(List *joinkeys, List *pathkey,
		 int which_subkey);
static List *new_join_pathkey(List *subkeys,
		 List *considered_subkeys, List *join_rel_tlist,
		 List *joinclauses);
static List *new_matching_subkeys(Var *subkey, List *considered_subkeys,
		 List *join_rel_tlist, List *joinclauses);

/****************************************************************************
 *     	KEY COMPARISONS
 ****************************************************************************/

/*    
 * match-pathkeys-joinkeys--
 *    Attempts to match the keys of a path against the keys of join clauses.
 *    This is done by looking for a matching join key in 'joinkeys' for
 *    every path key in the list 'pathkeys'. If there is a matching join key
 *    (not necessarily unique) for every path key, then the list of 
 *    corresponding join keys and join clauses are returned in the order in 
 *    which the keys matched the path keys.
 *    
 * 'pathkeys' is a list of path keys:
 * 	( ( (var) (var) ... ) ( (var) ... ) )
 * 'joinkeys' is a list of join keys:
 * 	( (outer inner) (outer inner) ... )
 * 'joinclauses' is a list of clauses corresponding to the join keys in
 * 	'joinkeys'
 * 'which-subkey' is a flag that selects the desired subkey of a join key
 * 	in 'joinkeys'
 *    
 * Returns the join keys and corresponding join clauses in a list if all
 * of the path keys were matched:
 * 	( 
 * 	 ( (outerkey0 innerkey0) ... (outerkeyN innerkeyN) )
 * 	 ( clause0 ... clauseN ) 
 * 	)
 * and nil otherwise.
 *    
 * Returns a list of matched join keys and a list of matched join clauses
 * in matchedJoinClausesPtr.  - ay 11/94
 */
List *
match_pathkeys_joinkeys(List *pathkeys,
			List *joinkeys,
			List *joinclauses,
			int which_subkey,
			List **matchedJoinClausesPtr)
{
    List *matched_joinkeys = NIL;
    List *matched_joinclauses = NIL;
    List *pathkey = NIL;
    List *i = NIL;
    int matched_joinkey_index = -1;
    
    foreach(i, pathkeys) {
	pathkey = lfirst(i);
	matched_joinkey_index = 
	    match_pathkey_joinkeys(pathkey, joinkeys, which_subkey);
	
	if (matched_joinkey_index != -1 ) {
	    List *xjoinkey = nth(matched_joinkey_index,joinkeys);
	    List *joinclause = nth(matched_joinkey_index,joinclauses);
	    
	    /* XXX was "push" function */
	    matched_joinkeys = lappend(matched_joinkeys,xjoinkey);
	    matched_joinkeys = nreverse(matched_joinkeys);
	    
	    matched_joinclauses = lappend(matched_joinclauses,joinclause);
	    matched_joinclauses = nreverse(matched_joinclauses);
	    joinkeys = LispRemove(xjoinkey,joinkeys);
	} else {
	    return(NIL);
	} 
	
    }
    if(matched_joinkeys==NULL ||
       length(matched_joinkeys) != length(pathkeys)) {
	return NIL;
    }

    *matchedJoinClausesPtr = nreverse(matched_joinclauses);
    return (nreverse(matched_joinkeys));
}

/*    
 * match-pathkey-joinkeys--
 *    Returns the 0-based index into 'joinkeys' of the first joinkey whose
 *    outer or inner subkey matches any subkey of 'pathkey'.
 */
static int
match_pathkey_joinkeys(List *pathkey,
		       List *joinkeys,
		       int which_subkey) 
{
    Var *path_subkey;
    int pos;
    List *i = NIL;
    List *x = NIL;
    JoinKey *jk;
    
    foreach(i, pathkey) {
	path_subkey = (Var *)lfirst(i);
	pos = 0;
	foreach(x, joinkeys) {
	    jk = (JoinKey*)lfirst(x);
	    if(var_equal(path_subkey,
			 extract_subkey(jk, which_subkey)))
		return(pos);
	    pos++;
	}
    }
    return(-1);    /* no index found   */
}

/*    
 * match-paths-joinkeys--
 *    Attempts to find a path in 'paths' whose keys match a set of join
 *    keys 'joinkeys'.  To match,
 *    1. the path node ordering must equal 'ordering'.
 *    2. each subkey of a given path must match(i.e., be(var_equal) to) the
 *       appropriate subkey of the corresponding join key in 'joinkeys',
 *       i.e., the Nth path key must match its subkeys against the subkey of
 *       the Nth join key in 'joinkeys'.
 *    
 * 'joinkeys' is the list of key pairs to which the path keys must be 
 * 	matched
 * 'ordering' is the ordering of the(outer) path to which 'joinkeys'
 * 	must correspond
 * 'paths' is a list of(inner) paths which are to be matched against
 * 	each join key in 'joinkeys'
 * 'which-subkey' is a flag that selects the desired subkey of a join key
 * 	in 'joinkeys'
 *    
 * Returns the matching path node if one exists, nil otherwise.
 */
static bool
every_func(List *joinkeys, List *pathkey, int which_subkey)
{
    JoinKey *xjoinkey;
    Var *temp;
    Var *tempkey = NULL;
    bool found = false;
    List *i = NIL;
    List *j = NIL;
    
    foreach(i,joinkeys) {
	xjoinkey = (JoinKey*)lfirst(i);
	found = false;
	foreach(j,pathkey) {
	    temp = (Var*)lfirst((List*)lfirst(j));
	    if(temp == NULL) continue;
	    tempkey = extract_subkey(xjoinkey,which_subkey);
	    if(var_equal(tempkey, temp)) {
		found = true;
		break;
	    }
	}
	if(found == false)
	    return(false);
    }
    return(found);
}


/*
 * match_paths_joinkeys -
 *    find the cheapest path that matches the join keys
 */
Path *
match_paths_joinkeys(List *joinkeys,
		     PathOrder *ordering,
		     List *paths,
		     int which_subkey)
{
    Path *matched_path = NULL ;
    bool key_match = false;
    List *i = NIL;

    foreach(i,paths) {
	Path *path = (Path*)lfirst(i);

	key_match = every_func(joinkeys, path->keys, which_subkey);
	
	if (equal_path_path_ordering(ordering,
				    &path->p_ordering) &&
	    length(joinkeys) == length(path->keys) &&
	    key_match) {

	    if (matched_path) {
		if (path->path_cost < matched_path->path_cost)
		    matched_path = path;
	    } else {
		matched_path = path;
	    }
	}
    }
    return matched_path;
}



/*    
 * extract-path-keys--
 *    Builds a subkey list for a path by pulling one of the subkeys from
 *    a list of join keys 'joinkeys' and then finding the var node in the
 *    target list 'tlist' that corresponds to that subkey.
 *    
 * 'joinkeys' is a list of join key pairs
 * 'tlist' is a relation target list
 * 'which-subkey' is a flag that selects the desired subkey of a join key
 * 	in 'joinkeys'
 *    
 * Returns a list of pathkeys: ((tlvar1)(tlvar2)...(tlvarN)).
 * [I've no idea why they have to be list of lists. Should be fixed. -ay 12/94]
 */
List *
extract_path_keys(List *joinkeys,
		  List *tlist,
		  int which_subkey)
{
    List *pathkeys = NIL;
    List *jk;
    
    foreach(jk, joinkeys) {
	JoinKey *jkey = (JoinKey*)lfirst(jk);
	Var *var, *key;
	List *p;

	/*
	 * find the right Var in the target list for this key
	 */
	var = (Var*)extract_subkey(jkey, which_subkey);
	key = (Var*)matching_tlvar(var, tlist);

	/*
	 * include it in the pathkeys list if we haven't already done so
	 */
	foreach(p, pathkeys) {
	    Var *pkey = lfirst((List*)lfirst(p));	/* XXX fix me */
	    if (key == pkey)
		break;
	}
	if (p!=NIL)
	    continue;	/* key already in pathkeys */

	pathkeys =
	    lappend(pathkeys, lcons(key,NIL));
    }
    return(pathkeys);
}


/****************************************************************************
 *     	NEW PATHKEY FORMATION
 ****************************************************************************/

/*    
 * new-join-pathkeys--
 *    Find the path keys for a join relation by finding all vars in the list
 *    of join clauses 'joinclauses' such that:
 *    	(1) the var corresponding to the outer join relation is a
 *    	    key on the outer path
 *    	(2) the var appears in the target list of the join relation
 *    In other words, add to each outer path key the inner path keys that
 *    are required for qualification.
 *    
 * 'outer-pathkeys' is the list of the outer path's path keys
 * 'join-rel-tlist' is the target list of the join relation
 * 'joinclauses' is the list of restricting join clauses
 *    
 * Returns the list of new path keys. 
 *    
 */
List *
new_join_pathkeys(List *outer_pathkeys,
		  List *join_rel_tlist,
		  List *joinclauses)
{	
    List *outer_pathkey = NIL;
    List *t_list = NIL;
    List *x;
    List *i = NIL;
    
    foreach(i, outer_pathkeys) {
	outer_pathkey = lfirst(i);
	x = new_join_pathkey(outer_pathkey, NIL, 
			     join_rel_tlist,joinclauses);
	if (x!=NIL) {
	    t_list = lappend(t_list, x);
	}
    }
    return(t_list);
}

/*    
 * new-join-pathkey--
 *    Finds new vars that become subkeys due to qualification clauses that
 *    contain any previously considered subkeys.  These new subkeys plus the
 *    subkeys from 'subkeys' form a new pathkey for the join relation.
 *    
 *    Note that each returned subkey is the var node found in
 *    'join-rel-tlist' rather than the joinclause var node.
 *    
 * 'subkeys' is a list of subkeys for which matching subkeys are to be
 * 	found
 * 'considered-subkeys' is the current list of all subkeys corresponding
 * 	to a given pathkey
 *    
 * Returns a new pathkey(list of subkeys).
 *    
 */
static List *
new_join_pathkey(List *subkeys,
		 List *considered_subkeys,
		 List *join_rel_tlist,
		 List *joinclauses)
{
    List *t_list = NIL;
    Var *subkey;
    List *i = NIL;
    List *matched_subkeys = NIL;
    Expr *tlist_key = (Expr*)NULL;
    List *newly_considered_subkeys = NIL;
    
    foreach (i, subkeys) {
	subkey = (Var *)lfirst(i);
	if(subkey == NULL)
	    break;    /* XXX something is wrong */
	matched_subkeys = 
	    new_matching_subkeys(subkey,considered_subkeys,
				 join_rel_tlist,joinclauses);
	tlist_key = matching_tlvar(subkey,join_rel_tlist);
	newly_considered_subkeys = NIL;
	
	if (tlist_key) {
	    if(!member(tlist_key, matched_subkeys))
		newly_considered_subkeys = lcons(tlist_key,
						 matched_subkeys);
	} 
	else {
	    newly_considered_subkeys = matched_subkeys;
	} 
	
	considered_subkeys = 
	    append(considered_subkeys, newly_considered_subkeys); 

	t_list = nconc(t_list,newly_considered_subkeys);
    }
    return(t_list);
}

/*    
 * new-matching-subkeys--
 *    Returns a list of new subkeys:
 *    (1) which are not listed in 'considered-subkeys'
 *    (2) for which the "other" variable in some clause in 'joinclauses' is
 *        'subkey'
 *    (3) which are mentioned in 'join-rel-tlist'
 *    
 *    Note that each returned subkey is the var node found in
 *    'join-rel-tlist' rather than the joinclause var node.
 *    
 * 'subkey' is the var node for which we are trying to find matching
 * 	clauses
 *    
 * Returns a list of new subkeys.
 *
 */
static List *
new_matching_subkeys(Var *subkey,
		     List *considered_subkeys,
		     List *join_rel_tlist,
		     List *joinclauses)
{
    Expr *joinclause = NULL;
    List *t_list = NIL;
    List *temp = NIL;
    List *i = NIL;
    Expr *tlist_other_var = (Expr *)NULL;
    
    foreach(i,joinclauses) {
	joinclause = lfirst(i);
	tlist_other_var = 
	    matching_tlvar(other_join_clause_var(subkey,joinclause),
			   join_rel_tlist);
	
	if(tlist_other_var && 
	   !(member(tlist_other_var,considered_subkeys))) {

	    /* XXX was "push" function  */
	    considered_subkeys = lappend(considered_subkeys,
					  tlist_other_var);

	    /* considered_subkeys = nreverse(considered_subkeys); 
	       XXX -- I am not sure of this. */
	    
	    temp = lcons(tlist_other_var, NIL);
	    t_list = nconc(t_list,temp);
	} 
    }
    return(t_list);
}
